1. Field of the Invention
The present invention relates to an alkaline storage battery such as a nickel-hydrogen storage battery, a nickel-cadmium storage battery and the like provided with a group of spiral electrodes composed of positive and negative electrode plates spirally wound with a separator interposed therebetween. More particularly, the present invention is concerned with a conductive connection between a group of spiral electrodes and a current-collector and a conductive connection between the group of spiral electrodes and a metallic cell casing.
2. Description of the Prior Art
In a manufacturing process of an alkaline storage battery such as a nickel-hydrogen storage battery or a nickel-cadmium storage battery, a group of spiral electrodes is composed of positive and negative electrode plates spirally wound with a separator interposed therebetween, and a positive current-collector is welded to the upper end of the positive electrode plate while a negative current-collector is welded to the bottom of the negative electrode plate. Thereafter, the negative current-collector is electrically connected to a negative terminal in the form of a metallic cell casing, while the positive current-collector is electrically connected to a positive terminal in the form of a closure element. In the case that the positive current-collector of the group of spiral electrodes is welded to the closure element while the negative current-collector is electrically connected to the bottom of the metallic cell casing, current distribution between the positive electrode plate and positive terminal (or closure element) and between the negative electrode plate and negative terminal (or cell casing) is uniformed to enhance a high-rate discharging characteristic of the storage battery.
In the alkaline storage battery, with the negative terminal is in the form of the metallic cell casing, an internal short-circuit will occur if the positive current-collector is brought into contact with the cell casing. It is, therefore, required to determine the size of the positive current-collector in an extent where the positive current-collector does not contact with the cell casing. On the other hand, any internal short-circuit does occur even if the negative current-collector is brought into contact with the cell casing. However, in the case that the outer diameter of the negative current-collector is determined substantially equal to the inner diameter of the cell casing, it becomes difficult to insert the group of spiral electrodes into the cell casing. If the negative current-collector was not welded to the group of spiral electrodes in an accurate position, the group of spiral electrodes would not be couple within the cell casing. For this reason, it is required to determine the size of the negative current-collector in an extent where the negative current-collector does not contact with the cell casing.
In the case that the size of the negative current-collector is determined to avoid contact with the cell casing, there will occur a non-welded portion of the negative current-collector in a position to be welded to the negative electrode plate. If such a non-welded portion is caused on the negative current-collector, the current distribution on a current collecting path between the negative current-collector and negative electrode plate becomes uneven resulting in drop of the battery voltage at the non-welded portion. The voltage drop does not cause any problem when the battery is charged and discharged at a small current. However, when the battery is charged and discharged at a large current of scores of amperes to hundreds of amperes, the battery voltage greatly drops due to a resistance at the non-welded portion, resulting in drop of the operation voltage. This causes deterioration of the high-rate discharging characteristic of the storage battery. As the reaction heat of the nickel-hydrogen storage battery at charging is smaller than that of a nickel-cadmium storage battery, the temperature rise of the battery becomes large due to the influence of joule-heat, resulting in an increase of the internal pressure of the battery at charging.
It is, therefore, a primary object of the present invention to provide an alkaline storage battery capable of enhancing the current collecting property of the negative current-collector even if a non-welded portion is caused on the current-collector to be welded or connected to the bottom of the cell casing. In the case that the present invention is adapted to a nickel-hydrogen storage battery, joule heat of the battery can be lowered by enhancement of the current collecting property of the negative current-collector. This is effective to suppress a temperature rise in the battery during charging and uniform reaction in the battery, thereby suppressing a rise in internal battery pressure.
According to the present invention, the object is accomplished by providing an alkaline storage battery including a group of spiral electrodes composed of positive and negative electrode plates spirally wound with a separator interposed therebetween and contained in a bottomed metallic cell casing used as an external terminal, wherein the group of spiral electrodes is formed at its central portion with a space defined by a winding core during the winding process of the electrode plates and is provided with a first current-collector welded to an upper end of one of the electrode plates (for example, the positive electrode plate) and a second current-collector welded to a lower end of the other electrode plate (for example, the negative electrode plate), wherein the second current-collector is welded to an internal surface of the bottom of the cell casing without being welded to an end portion of the other plate located at the outermost periphery of the group of spiral electrodes, and wherein the other electrode plate (for example, the negative electrode plate) at the outermost periphery of the group of spiral electrodes is pressed into contact with an internal peripheral wall of the cell casing.
In the alkaline storage battery described above, current collection at the electrode plate (for example, the negative electrode plate) pressed into contact with the internal peripheral wall is uniformed to reduce the voltage drop of the battery thereby to enhance a high-rate discharge characteristic of this kind of alkaline storage battery. Additionally, in the case that the core plate of the electrode plate (for example, the negative electrode plate) is pressed into contact with the internal peripheral wall of the cell casing, resistance at a surface in contact with the cell casing is further decreased toreduce the voltage drop of the battery thereby to further enhance the high-rate discharge characteristic of this kind of alkaline storage battery.
According to an aspect of the present invention, there is provided an alkaline storage battery including a group of spiral electrodes composed of positive and negative electrode plates spirally wound with a separator interposed therebetween and contained in a bottomed metallic cell casing used as an external terminal, wherein the group of spiral electrodes is formed without any space at its central portion and is provided with a first current-collector welded to an upper end of one of the electrode plates (for example, the positive electrode plate) and a second current-collector welded to a lower end of the other electrode plate (for example, the negative electrode plate), wherein the second current-collector is retained in contact with an internal surface of the bottom of the cell casing without being welded thereto and to an end portion of the other plate located at the outermost periphery of the group of spiral electrodes, and wherein the other electrode plate (for example, the negative electrode plate) at the outermost periphery of the group of spiral electrodes is pressed into contact with an internal peripheral wall of the cell casing.
With such an arrangement of the alkaline storage battery described above, the capacity of the battery can be increased, and the resistance at a surface of the electrode plate (for example, the negative electrode plate) in contact with the cell casing is decreased to reduce the voltage drop of the battery thereby to enhance the high-rate discharge characteristic of this kind of alkaline storage battery.